The present invention is directed generally to power supplies. Specifically, the invention is directed to plug-in transformer power supplies.
Many of today's office appliances use direct current (DC) motors because they are mass produced and, as a result, are less expensive and readily available for many applications. Consequently, there is a great need for developing a highly efficient plug-in transformer power supply to operate these motors.
While many office machines use 24 volts direct current (VDC) power, output power generally is limited in prior art power supplies.
Additionally, since 12 volt rechargeable batteries have become standard in the industry, plug-in transformer power supplies generally are used to recharge these batteries. However, a limitation of the prior art plug-in power supplies is that the 12 volt units currently available do not output more than 18 watts. In addition to the foregoing, industry standards such as those established by Underwriters Laboratories (UL), Chicago, Ill. set forth operating characteristics for various classes of power supplies. In meeting their standards, it often is necessary to employ over-rated components so that the resulting product meets the standards.
The UL standards include UL Class 2 power units defined by UL standard 1310 and Table 28.1 dated Feb. 28, 1989; and UL Class 105 (a/k/a Class A) and UL Class 130 (a/k/a Class B) insulations defined by Table 31.1 of UL 1310 dated Aug. 21, 1992, all of which are incorporated herein by reference.